Display screen or portion thereof with transitional graphical user interface



FIG. 1 is the first image in a sequence of a display screen or portionthereof with transitional graphical user interface showing my newdesign;

FIG. 2 is the second image thereof; and,

FIG. 3 is the third image thereof.

The outer broken lines in the figures depict the display screen orportion thereof and form no part of the claimed design.

The remaining broken lines in the figures depict portions of thetransitional graphical user interface that form no part of the claimeddesign.

The appearance of the transitional graphical user interface sequentiallytransitions between the images shown in FIGS. 1 through 3. The processor period in which one image transitions to another forms no part of theclaimed design.

CLAIM I claim the ornamental design for a display screen or portionthereof with transitional graphical user interface, as shown anddescribed.